Increases the UT coverage of db_replicator.py

Adds 20 unit tests to increase the coverage of db_replicator.py
from 71% to 90%

Change-Id: Ia63cb8f2049fb3182bbf7af695087bfe15cede54
Closes-Bug: #948179
Merge "Increases the UT coverage of db_replicator.py"